In automation technology (process automation, manufacturing automation), field devices are often applied, which serve for registering and/or influencing process variables. Examples of such field devices for process automation technology are fill level measuring devices, mass flow measuring devices, pressure, and temperature, measuring devices, pH, and redox-potential, measuring devices, conductivity measuring devices, etc., which, as sensors, register the corresponding process variables, fill level, flow, pressure, temperature, pH-value, or conductivity value.
Serving for influencing process variables actuators are, e.g. valves, which control the flow of a liquid in a pipeline section, or pumps, which change the fill level in a container.
A large number of such field devices are produced and sold by the firm, Endress+Hauser®.
Frequently, field devices are connected with superordinated units via fieldbus systems (Profibus®, Foundation® Fieldbus, HART®, etc.). These superordinated units serve, on the basis of corresponding programs, for process control, process visualizing, for servicing the field devices and for plant management (asset-management).
The integration of field devices into such applications occurs via device descriptions. These device descriptions are provided by the device manufacturers, in order that the applications can interpret e.g. the meaning of output delivered from the field devices.
There are different device descriptions for the different fieldbus systems (HART device descriptions, Fieldbus Foundation device descriptions, Profibus device descriptions).
On the basis of the cooperation of the Fieldbus Foundation (FF), the HART Communication Foundation (HCF) and the Profibus Nutzerorganisation (User Organization) (PNO), an electronic device description (EDD) was created, which is defined in the standard IEC 61804-2.
For servicing the field devices, corresponding operating programs (operating tools) are necessary, which run either self-sufficiently in the superordinated units (FieldCare of Endress+Hauser, Pactware, AMS of Fisher-Rosemount, PDM of Siemens) or integrated in control system applications (Siemens' PCS7, ABB's Symphony, Emerson's Delta V).
For comfortable servicing of the field devices, recently, special device descriptions, so called device DTMs (Device Type Manager), which correspond to the FDT (Field Device Tool) specifications, have become obtainable. The FDT specifications were developed as an industrial standard by PNO (Profibus User Organisation) in cooperation with ZVEI (Zentralverband Elektrotechnik- and Elektroindustrie, or German Electrical and Electronics Manufacturers' Association). The current FDT-Specification 1.2.1, including the addendum for “Foundation Fieldbus” communication, is obtainable from ZVEI, or PNO, or the FDT-Group.
Many field device manufacturers already deliver device DTMs for their field devices. The device DTMs encapsulate functions and variables of a given field device and provide, most often, a graphical user interface.
Device DTMs are software components, which, however, are not independently executable. As runtime environment, the device DTMs require a frame application (also referred to as an FDT-frame), e.g. FieldCare of the firm, Endress+Hauser. The frame application and the corresponding device DTMs represent an operating program for field devices, which enables very comfortable accessing of field devices (e.g. device parameters, measured values, status information, etc.), as well as the invoking of special functions (e.g. diagnosis).
The providing of device DTMs is, however, associated with considerable effort for the field device manufacturers. For the case, in which the program code must be newly written for a device DTM, such can, depending on the complexity of the field device, require a developmental time of a number of weeks.
Once device DTMs are done, they must be extensively tested, in order to assure, that they will work without problem with the relevant field device, or device type, and reflect its functionality correctly.
These tests also have a safety related aspect, since, via device DTMs, also safety-critical parameters can be adjusted in field devices. Secure and reliable servicing is an essential requirement in the development of device DTMs.
If the device software of a field device is changed, then, frequently, also the device DTM for the field device must be rewritten, which leads to additional effort on the part of the field device manufacturers.
In the development of device DTMs, field device manufacturers frequently start with already present, device descriptions (e.g. HART DDs). The firm, CodeWrights, in Karlsruhe, Germany produces device DTMs in large number based on HART-DDs. Complex functionalities (such as e.g. complex calculations for a device diagnosis) can, however, not be recreated with the assistance of HART-DDs. These functionalities are, thus, missing in the corresponding device DTMs. If these complex functionalities should also be integrated into the device DTMs, a complex reworking of the corresponding program code is necessary.
An important requirement in the case of device servicing is offline servicing. In such case, a field device, which is to be serviced, is either not at all physically connected with the superordinated unit in which the operating program is running, or it is not accessible from the operating program, because it is still not integrated into the fieldbus system. In spite of this, the user would like to already input device parameters for this field device.
In order to enable a complete offline servicing, very great effort is necessary in the creation of the device DTMs. As a rule, no hundred percent offline servicing can be assured with conventional device DTMs.